Silicon-carbon composite material with internal pore structure and its preparation method and application

Abstract

A long-cycle and low-expansion silicon-carbon composite material with an internal pore structure includes a silicon source, a closed pore, a filling layer and a carbon coating layer. The closed pore is a large closed pore or composed of a plurality of small closed pores and the filling layer is a carbon filling layer. The invention provides a long-cycle and low-expansion silicon-carbon composite material with an internal pore structure which is reduced in volume expansion effect and improved in volume effect of cycle performance. The invention further provides a preparation method and application of a long-cycle and low-expansion silicon-carbon composite material with an internal pore structure. The process is simple. The volume expansion effect being reduced and the cycle performance being improved are of great significance to the application of silicon-based materials in lithium-ion batteries.

What is claimed is: 
     
         1 . A silicon-carbon composite material with an internal pore structure, consisting of a silicon source, a closed pore, a filling layer and a carbon coating layer, wherein the closed pore is a large closed pore or composed of a plurality of small closed pores, and the filling layer is a carbon filling layer filled among particles of the silicon source, and the carbon coating layer encloses the silicon source, the closed pore and the filling layer therein. 
     
     
         2 . The silicon-carbon composite material with an internal pore structure according to  claim 1 , wherein an outer surface of the closed pore comprises a carbon layer, a size of the large closed pore is larger than 50 nm but less than or equal to 8 μm, and a size of the small closed pore is larger than 10 nm but less than or equal to 50 nm. 
     
     
         3 . The silicon-carbon composite material with an internal pore structure according to  claim 1 , wherein the silicon source is any one or more of polycrystalline nano-silicon and amorphous nano-silicon. 
     
     
         4 . The silicon-carbon composite material with an internal pore structure according to  claim 1 , wherein when the silicon source is polycrystalline nano-silicon, a crystal size of the polycrystalline nano-silicon is 1 nm to 40 nm. 
     
     
         5 . The silicon-carbon composite material with an internal pore structure according to  claim 1 , wherein the silicon source is SiOx, where X is between 0 and 0.8; a particle diameter D50 of the silicon source is less than 200 nm. 
     
     
         6 . A preparation method of a silicon-carbon composite material with an internal pore structure, comprising the following steps:
 S0, mixing and dispersing a silicon source, a dispersant, and a pore-former in a solvent evenly, and performing spray drying treatment to obtain a precursor A;   S1, carbonizing the precursor A to obtain a precursor B;   S2, mechanically mixing and fusing the precursor B and an organic carbon source to obtain a precursor C;   S3, carrying out high-temperature, vacuum or pressurized carbonization on the precursor C to obtain a precursor D;   S4, crushing and sieving the precursor D to obtain a precursor E; and   S5, carrying out carbon coating heat treatment on the precursor E to obtain the silicon-carbon composite material.   
     
     
         7 . The preparation method of silicon-carbon composite material with an internal pore structure according to  claim 6 , wherein the pore-former in step S0 is an organic substance insoluble or slightly soluble in the dispersant. 
     
     
         8 . The preparation method of a silicon-carbon composite material with an internal pore structure according to  claim 7 , wherein the pore-former comprises one or more of sucrose, glucose, citric acid, phenolic resin, epoxy resin, polyimide resin, pitch, polyvinyl alcohol, polypyrrole, polypyrrolidone, polyaniline, polyacrylonitrile, polydopamine, polyethylene, polypropylene, polyamide, polystyrene, polymethyl methacrylate, and polyvinyl chloride. 
     
     
         9 . The preparation method of a silicon-carbon composite material with an internal pore structure according to  claim 6 , wherein, in step S0, a ratio of the pore-former to the silicon source is 1% to 80%. 
     
     
         10 . An application of a silicon-carbon composite material with an internal pore structure, wherein the silicon-carbon composite material with an internal pore structure prepared by the preparation method according to  claim 6  is applied to lithium-ion batteries.